KR102356684B1 - Optical sensor and image sensor including graphene quantum dot - Google Patents

Abstract

An optical sensor and an image sensor including graphene quantum dots are disclosed. The disclosed photosensor includes a graphene quantum dot layer having a plurality of first graphene quantum dots associated with a first functional group and a plurality of second graphene quantum dots associated with a second functional group different from the first functional group. The absorption wavelength band of the photosensor can be adjusted according to the type of functional group bonded to each graphene quantum dot and the size of the graphene quantum dot.

Description

Optical sensor and image sensor including graphene quantum dot}

The disclosed embodiments relate to an optical sensor and an image sensor, and more particularly, to an optical sensor and an image sensor including graphene quantum dots to which a functional group is bonded.

Silicon semiconductors commonly used in photosensors and image sensors have significantly lower quantum efficiency in the infrared band compared to the quantum efficiency in the visible light band. Accordingly, there is an attempt to use graphene instead of a silicon semiconductor in optical sensors used for biometric authentication sensors, low-light sensitivity enhancement equipment, night vision goggles, autonomous driving sensors, and the like. Since graphene does not have a band gap, the optical sensor using graphene can theoretically detect not only visible light but also ultraviolet and infrared light.

Provided are an optical sensor and an image sensor including graphene quantum dots.

An optical sensor according to an embodiment includes a first electrode; a photodetector layer disposed on the first electrode; and a second electrode disposed on the photo-detecting layer, wherein the photo-detecting layer includes a plurality of first graphene quantum dots bonded to a first functional group and a plurality of first graphene quantum dots bonded to a second functional group different from the first functional group. It may include a graphene quantum dot layer having a second graphene quantum dot.

The first functional group is bonded to at least one of the carbons disposed at the edge of each first graphene quantum dot and the second functional group is bonded to at least one of the carbons disposed at the edge of each second graphene quantum dot. can

The first graphene quantum dots may be configured to absorb light of a first wavelength band, and the second graphene quantum dots may be configured to absorb light of a second wavelength band different from the first wavelength band.

The graphene quantum dot layer further includes a plurality of third graphene quantum dots combined with a third functional group different from the first and second functional groups, wherein the third graphene quantum dots are third different from the first and second wavelength bands. It may be configured to absorb light in a wavelength band.

For example, the first functional group and the second functional group are -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C=O)-, -F, -H, -CO-N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine, aniline, and PEG ( polyethylene glycol) may be included.

The first graphene quantum dots may have a first size, and the second graphene quantum dots may have a second size different from the first size.

The photodetecting layer may have a thickness in the range of, for example, 50 nm to 100 um.

The photodetection layer may further include a semiconductor layer disposed between the first electrode and the graphene quantum dot layer.

The semiconductor layer includes at least one semiconductor material from among a semiconductor material including silicon, a compound semiconductor material, an organic semiconductor material, and a two-dimensional material having a bandgap and a two-dimensional crystal structure, wherein the semiconductor material is the semiconductor layer. and a Schottky barrier may be formed between the first electrode.

An energy difference between a lowest unoccupied molecular orbital (LUMO) energy level of the graphene quantum dot layer and a valence band of the semiconductor layer may be smaller than an energy difference between a work function of the first electrode and a conduction band of the semiconductor layer.

The two-dimensional material may include, for example, a transition metal dichalcogenide, which is a compound of a transition metal and a chalcogen element.

For example, the transition metal is at least one of tin (Sn), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), hafnium (Hf), titanium (Ti), and rhenium (Re). Including one, the chalcogen element may include at least one of sulfur (S), selenium (Se), and tellurium (Te).

The semiconductor layer includes a first semiconductor layer disposed over the first electrode and a second semiconductor layer disposed over the first semiconductor layer, wherein the first semiconductor layer is doped to a first conductivity type and the second semiconductor layer is Silver may be doped with a second conductivity type that is electrically opposite to the first conductivity type.

The second electrode may be a transparent electrode having transmittance to light of a wavelength band to be detected.

In addition, the photosensor according to another embodiment, the first electrode; a semiconductor layer disposed on the first electrode; a graphene quantum dot layer disposed on the semiconductor layer; and a second electrode disposed on the graphene quantum dot layer, wherein the graphene quantum dot layer includes a plurality of first graphene quantum dots combined with a first functional group, and the material of the semiconductor layer includes the semiconductor layer and It may be chosen such that a Schottky barrier is formed between the first electrodes.

An energy difference between a lowest unoccupied molecular orbital (LUMO) energy level of the graphene quantum dot layer and a valence band of the semiconductor layer may be smaller than an energy difference between a work function of the first electrode and a conduction band of the semiconductor layer.

The graphene quantum dot layer further includes a plurality of second graphene quantum dots combined with a second functional group different from the first functional group, wherein the first graphene quantum dots are configured to absorb light of a first wavelength band The second graphene quantum dots may be configured to absorb light in a second wavelength band different from the first wavelength band.

The semiconductor layer includes a first semiconductor layer disposed over the first electrode and a second semiconductor layer disposed over the first semiconductor layer, wherein the first semiconductor layer is doped to a first conductivity type and the second semiconductor layer is Silver may be doped with a second conductivity type that is electrically opposite to the first conductivity type.

In addition, the photosensor according to another embodiment, the first electrode and the second electrode disposed to face each other; and a plurality of semiconductor layers and a plurality of graphene quantum dot layers alternately disposed between the first electrode and the second electrode, wherein the graphene quantum dot layer includes a plurality of first graphene quantum dots coupled to a first functional group Including, wherein the plurality of semiconductor layers include a first semiconductor layer disposed on the first electrode and a second semiconductor layer disposed between two graphene quantum dot layers, the material of the semiconductor layer being the semiconductor layer and It may be chosen such that a Schottky barrier is formed between the first electrodes.

The energy difference between the lowest unoccupied molecular orbital (LUMO) energy level of the graphene quantum dot layer and the valence band of the first semiconductor layer is smaller than the energy difference between the work function of the first electrode and the conduction band of the first semiconductor layer The energy difference between the highest occupied molecule orbital (HOMO) energy level of the graphene quantum dot layer and the conduction band of the second semiconductor layer is greater than the energy difference between the work function of the first electrode and the conduction band of the first semiconductor layer. can be small

The thickness of each second semiconductor layer may be selected such that tunneling occurs in each of the second semiconductor layers.

Meanwhile, an image sensor according to an embodiment includes a light sensing layer; and a signal processing layer that processes the optical signal detected by the optical sensing layer into an electrical signal, wherein the optical sensing layer includes a first optical detection layer that detects light in a first wavelength band, and a first wavelength band and a second detection layer for detecting light in a second wavelength band different from that, wherein the first photodetection layer includes a first graphene quantum dot layer having a plurality of first graphene quantum dots bonded to a first functional group and the second photodetection layer may include a second graphene quantum dot layer including a plurality of second graphene quantum dots combined with a second functional group different from the first functional group.

The light sensing layer includes a third graphene quantum dot layer having a plurality of third graphene quantum dots bonded to a third functional group different from the first and second functional groups, and a fourth functional group different from the first to third functional groups. It may further include a fourth graphene quantum dot layer having a plurality of fourth graphene quantum dots combined with.

The sizes of the first to fourth graphene quantum dots may be different from each other.

The photosensor and image sensor according to the disclosed embodiment include a photodetection layer using graphene quantum dots. Graphene quantum dots can not only efficiently absorb light in the infrared band like graphene, but also have a band gap like quantum dots. Accordingly, it is possible to reduce the noise of the photosensor by suppressing the dark current. In addition, by bonding a functional group to the edge of the graphene quantum dots, it is possible to prevent direct electrical contact between adjacent graphene quantum dots. Then the dark current can be further suppressed. In addition, it is possible to effectively control the absorption wavelength band according to the type of functional group bonded to the graphene quantum dot and the size of the graphene quantum dot.

1 is a cross-sectional view schematically showing a structure of an optical sensor according to an embodiment.
2 is a graph exemplarily showing a change in absorption characteristics of a photodetection layer according to a process temperature and thickness of a photodetection layer including graphene quantum dots.
3 is a cross-sectional view schematically illustrating a structure of an optical sensor according to another embodiment.
FIG. 4 is a graph exemplarily showing absorption characteristics of a photodetector layer of the photosensor shown in FIG. 3 .
5 is a cross-sectional view schematically showing a structure of an optical sensor according to another embodiment.
6A and 6B schematically show energy band diagrams of the photosensor shown in FIG. 5 .
7 is a cross-sectional view schematically illustrating a structure of an optical sensor according to another embodiment.
8 is a cross-sectional view schematically illustrating a structure of an optical sensor according to another embodiment.
9A is a cross-sectional view schematically illustrating a structure of one pixel of an image sensor according to an exemplary embodiment.
9B and 9C are plan views illustrating an arrangement of sub-pixels in one pixel of the image sensor illustrated in FIG. 9A .
10 is a cross-sectional view schematically illustrating a structure of one pixel of an image sensor according to another exemplary embodiment.
11 is a cross-sectional view schematically illustrating a structure of one pixel of an image sensor according to another exemplary embodiment.

Hereinafter, an optical sensor and an image sensor including graphene quantum dots will be described in detail with reference to the accompanying drawings. In the following drawings, the same reference numerals refer to the same components, and the size of each component in the drawings may be exaggerated for clarity and convenience of description. In addition, the embodiments described below are merely exemplary, and various modifications are possible from these embodiments. In addition, in the layer structure described below, the expression "upper" or "upper" may include not only directly on in contact but also on non-contacting.

1 is a cross-sectional view schematically showing a structure of an optical sensor according to an embodiment. Referring to FIG. 1 , a photosensor 10 according to an embodiment includes a first electrode 11 , a photodetection layer 12 disposed on the first electrode 11 , and a photodetection layer 12 disposed on the photodetection layer 12 . A second electrode 14 may be included. The first electrode 11 and the second electrode 14 may be made of any conductive material including metal, graphene, transparent conductive oxide or transparent conductive nitride. In particular, the second electrode 14 disposed in the light incident direction may be made of a transparent conductive material. That is, the second electrode 14 may be a transparent electrode having transmittance to light of a wavelength band to be detected.

The photodetecting layer 12 may include a plurality of graphene quantum dots 15 as a material for absorbing light to generate a photocurrent. 1 shows an enlarged structure of one graphene quantum dot 15 in the photodetection layer 12 . The graphene quantum dots 15 are graphene having a small size of about 2 nm to 20 nm, and may have the same characteristics as general quantum dots. For example, unlike general graphene, the graphene quantum dots 15 may have a band gap due to a quantum confinement effect, and the band gap may be adjusted according to their size. Accordingly, noise of the photosensor 10 can be reduced by suppressing a dark current generated while no light is incident. In addition, since the graphene quantum dots 15 have a two-dimensional structure, it may be easier to control the size and control the density per unit area compared to general quantum dots having a three-dimensional structure. Accordingly, the absorption wavelength band and sensitivity of the photodetector layer 12 can be easily adjusted.

In addition, the absorption characteristics of the photodetector layer 12 may be adjusted according to the process temperature of the photodetector layer 12 . The photodetection layer 12 may be formed by applying a paste including graphene quantum dots 15 on the first electrode 11 and then drying the paste by removing a solvent through heat treatment. In the process of forming the photodetecting layer 12 in this way, the absorption characteristics of the photodetecting layer 12 may be adjusted according to the heating temperature and heating time. For example, FIG. 2 is a graph exemplarily showing changes in the absorption characteristics of the photodetection layer 12 according to the process temperature and thickness of the photodetection layer 12 including the graphene quantum dots 15 . Referring to FIG. 2 , when the photodetection layer 12 has a thickness of 100 nm and the photodetection layer 12 is formed at a temperature of 300° C. Able to know. In particular, the change in absorption according to wavelength in the infrared band is small. For example, the photodetector layer 12 having a thickness of 100 nm and formed at a temperature of 300° C. exhibited an absorption coefficient of about 9354.2/cm for incident light having a wavelength of 850 nm, and an absorption coefficient of about 9354.2/cm for incident light having a wavelength of 2000 nm. It showed an absorption coefficient of about 8523.1/cm. In order to sufficiently increase the detection efficiency of incident light, the thickness of the light detection layer 12 may be selected within the range of 50 nm to 100 um.

Also, according to the present embodiment, the photodetection layer 12 may include graphene quantum dots 15 to which a functional group 16 is bonded. The functional group 16 may be bonded to at least one of carbons disposed on the edge of the graphene quantum dots 15 . By bonding the functional group 16 to the edge of the graphene quantum dots 15, direct electrical contact between the graphene quantum dots 15 adjacent to each other can be prevented. Then the dark current can be further suppressed. In addition, since the band gap of the graphene quantum dots 15 varies according to the type of the functional group 16 coupled to the graphene quantum dots 15 , the absorption wavelength band of the photodetection layer 12 can be effectively controlled. For example, the functional group 16 capable of binding to the graphene quantum dots 15 is -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -( C=O)-, -F, -H, -CO-N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine, aniline ( aniline), and at least one of polyethylene glycol (PEG). The band gap of the graphene quantum dots 15 to which the functional group 16 is bonded may have different values depending on the type of the functional group 16 described above. For example, when the functional group 16 bonded to the graphene quantum dots 15 is one of -NH ₂ , -OH, -COOH, -CHO, and -COCH ₃ , in general -NH ₂ > -OH > -CHO > -COCH ₃ > In the order of -COOH, the graphene quantum dots 15 may have a large band gap. The band gap and the absorption wavelength band are in inverse proportion to each other. Therefore, the functional group 16 having a corresponding band gap according to the desired absorption wavelength band may be coupled to the graphene quantum dots 15 . In addition, a plurality of identical functional groups 16 may be bonded to one graphene quantum dot 15 , but two or more different functional groups 16 may be bonded to one graphene quantum dot 15 .

3 is a cross-sectional view schematically showing the structure of the photosensor 20 according to another embodiment. Referring to FIG. 3 , the photodetection layer 22 may include at least two types of graphene quantum dots 15a , 15b , and 15c that respectively absorb light of different wavelength bands. For example, the photodetection layer 22 may include a plurality of first graphene quantum dots 15a bonded to a first functional group (A), and a plurality of second graphene quantum dots 15b bonded to a second functional group (B). , and a plurality of third graphene quantum dots 15c bonded to the third functional group (C). The first functional group (A) is bonded to at least one of the carbons disposed on the edge of each of the first graphene quantum dots (15a), and the second functional group (B) is the edge of each second graphene quantum dot (15b). It is bonded to at least one of the carbons disposed in , and the third functional group (C) is bonded to at least one of the carbons disposed at the edge of each third graphene quantum dot 15c. 3 shows three types of graphene quantum dots 15a, 15b, and 15c for convenience, the photodetection layer 22 may include only two types of graphene quantum dots or may include four or more types of graphene quantum dots. .

In addition, the first graphene quantum dots 15a, the second graphene quantum dots 15b, and the third graphene quantum dots 15c may have different sizes. For example, the first graphene quantum dot 15a has a first functional group A and a first size to absorb light of a first wavelength band, and the second graphene quantum dot 15b has a second size different from the first wavelength band. It may have a second functional group (B) different from the first functional group (B) and a second size different from the first size so as to absorb light in a wavelength band, and the third graphene quantum dot 15c has the first and second wavelengths. It may have a third functional group (C) different from the first and second functional groups (A and B) and a third size different from the first and second sizes so as to absorb light of a third wavelength band different from that of the first and second functional groups. Here, the first to third functional groups (A, B, C) are each of the above-mentioned -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C =O)-, -F, -H, -CO-N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine, aniline ), and PEG (polyethylene glycol).

FIG. 4 is a graph exemplarily showing absorption characteristics of the light detection layer 22 of the photosensor 20 shown in FIG. 3 . For example, the photodetector layer 22 may include a plurality of first graphene quantum dots 15a configured to absorb light in a blue wavelength band B, and a plurality of second graphene quantum dots 15a configured to absorb light in a green wavelength band G. The graphene quantum dots 15b and a plurality of third graphene quantum dots 15c configured to absorb light in the red wavelength band R may be included. Through the combination of various types of graphene quantum dots 15a, 15b, and 15c having different absorption characteristics, the photodetection layer 22 may have a constant absorption rate in the visible ray band. In addition, if the photodetection layer 22 further includes a plurality of graphene quantum dots configured to absorb light in the infrared band, the photodetection layer 22 is relatively over a wide spectral range including the visible light band and the infrared band. It may have a uniform absorption rate.

5 is a cross-sectional view schematically showing a structure of an optical sensor according to another embodiment. Referring to FIG. 5 , the photosensor 30 includes a first electrode 11 , a photodetection layer 32 disposed on the first electrode 11 , and a second electrode 14 disposed on the photodetection layer 32 . ) may be included. In addition, the photodetection layer 32 may include a semiconductor layer 33 disposed on the first electrode 11 and a graphene quantum dot layer 34 disposed on the semiconductor layer 33 . Here, the graphene quantum dot layer 34 may include a plurality of graphene quantum dots, such as the photodetection layer 12 shown in FIG. 1 or the photodetection layer 22 shown in FIG. 3 . 1 and 3 , the graphene quantum dot layer 34 may include at least one type of graphene quantum dots each bonded to at least one functional group. That is, the description of the photodetecting layers 12 and 22 shown in FIGS. 1 and 3 may be directly applied to the graphene quantum dot layer 34 . In this regard, the photodetecting layers 12 and 22 shown in FIGS. 1 and 3 can be considered to include one graphene quantum dot layer.

The semiconductor layer 33 serves to form a Schottky barrier at the interface between the semiconductor layer 33 and the first electrode 11 . Due to such a Schottky barrier, it is possible to prevent electrons from easily moving from the first electrode 11 to the graphene quantum dot layer 34 through the semiconductor layer 33 while light is not incident. Accordingly, the semiconductor layer 33 can further suppress the dark current.

For example, FIGS. 6A and 6B exemplarily show energy band diagrams of the photosensor 30 shown in FIG. 5 . In particular, FIG. 6A is an energy band diagram while voltage is applied to the first and second electrodes 11 and 14 and no light is incident on the photosensor 30, and FIG. 6B is the first and second electrodes 11 and 11 , 14) is an energy band diagram during which a voltage is applied and light is incident on the photosensor 30 . It is assumed that the first and second electrodes 11 and 14 in FIGS. 6A and 6B are made of graphene. First, referring to FIG. 6A , since the energy difference ΦB between the work function of the first electrode 11 and the conduction band of the semiconductor layer 33 is large, electrons are transferred from the first electrode 11 to the semiconductor layer ( 33) is almost never moved. Accordingly, it is possible to suppress the dark current in a state in which no light is incident on the photosensor 30 . On the other hand, as shown in FIG. 6B , when light is incident on the photosensor 30 , electrons e and holes h are generated in the graphene quantum dot layer 34 so that a photocurrent flows. For example, electrons e generated in the graphene quantum dot layer 34 may move to the second electrode 14 according to an electric field applied between the first electrode 11 and the second electrode 14 . In addition, holes h generated in the graphene quantum dot layer 34 may pass through the semiconductor layer 33 to the first electrode 11 . When the material of the semiconductor layer 33 is selected so that the energy difference between the lowest unoccupied molecular orbital (LUMO) energy level of the graphene quantum dot layer 34 and the valence band of the semiconductor layer 33 is small, graphene quantum dots Holes h generated in the layer 34 may easily move to the semiconductor layer 33 . For example, the energy difference between the LUMO energy level of the graphene quantum dot layer 34 and the valence band of the semiconductor layer 33 is the energy difference between the work function of the first electrode 11 and the conduction band of the semiconductor layer 33 . may be smaller than For example, the energy difference between the LUMO energy level of the graphene quantum dot layer 34 and the valence band of the semiconductor layer 33 is the energy difference between the work function of the first electrode 11 and the conduction band of the semiconductor layer 33 . It can be 1/2 of or less than that.

As the material of the semiconductor layer 33, any semiconductor material capable of satisfying the above-described relationship between the semiconductor layer 33 and the first electrode 11 and between the semiconductor layer 33 and the graphene quantum dot layer 34 may be used. can be used For example, in addition to a conventional semiconductor material such as silicon or germanium, a compound semiconductor material, an organic semiconductor material, or a two-dimensional semiconductor material having a band gap and a two-dimensional crystal structure may be used as the material of the semiconductor layer 33 . In particular, since the graphene quantum dot layer 34 has graphene quantum dots of a two-dimensional structure, the use of a two-dimensional semiconductor material as the semiconductor layer 33 increases the alignment of a plurality of graphene quantum dots of the graphene quantum dot layer 34 . can be advantageous For example, as a two-dimensional semiconductor material, there is a transition metal dichalcogenide (TMD), which is a typical compound of a transition metal and a chalcogen element. The transition metal is, for example, at least one of tin (Sn), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), hafnium (Hf), titanium (Ti), and rhenium (Re). Including one, the chalcogen element may include, for example, at least one of sulfur (S), selenium (Se), and tellurium (Te). For example, transition metal _{dichalcogenides are MoS 2} , WS ₂ , TaS ₂ , HfS ₂ , ReS ₂ , TiS ₂ , NbS ₂ , SnS ₂ , MoSe ₂ , WSe ₂ , TaSe ₂ , HfSe ₂ , ReSe ₂ , TiSe ₂ , NbSe ₂ , SnSe ₂ , MoTe ₂ , WTe ₂ , TaTe ₂ , HfTe ₂ , ReTe ₂ , TiTe ₂ , NbTe ₂ , SnTe ₂ may be included. In addition to transition metal dichalcogenides, there are various two-dimensional semiconductor materials. For example, the 2D semiconductor material is h-BN (hexagonal BN), phosphorene, TiOx, NbOx, MnOx, VaOx, MnO ₃ , TaO ₃ , WO ₃ , MoCl ₂ , CrCl ₃ , RuCl ₃ , BiI ₃ , PbCl ₄ , GeS, GaS, GeSe, GaSe, PtSe ₂ , In ₂ Se ₃ , GaTe, InS, InSe, InTe, and the like. h-BN is a hexagonal crystal structure formed by combining boron (B) and nitrogen (N). Phosphorine is a two-dimensional allotrope of black phosphorus.

In addition, the semiconductor layer 33 may serve to absorb light in addition to suppressing the dark current. 5 shows that the semiconductor layer 33 is disposed directly on the first electrode 11 and the graphene quantum dot layer 34 is disposed immediately below the transparent second electrode 14, but the semiconductor layer 33 The positions of the graphene quantum dot layer 34 and the graphene quantum dot layer 34 may be interchanged. That is, the graphene quantum dot layer 34 is disposed on the first electrode 11 , the semiconductor layer 33 is disposed on the graphene quantum dot layer 34 , and the second electrode 14 is transparent on the semiconductor layer 33 . This may be arranged. In this case, a Schottky barrier is formed at the interface between the semiconductor layer 33 and the second electrode 14 .

In addition, when the semiconductor layer 33 is disposed on the graphene quantum dot layer 34 , the semiconductor layer 33 absorbs light of some wavelength band among incident light and transmits light of another wavelength band. to reach the graphene quantum dot layer 34 . For example, the semiconductor layer 33 may be made of a semiconductor material to absorb light in a visible light band and transmit light in an infrared band. In this case, the graphene quantum dot layer 34 may be configured to absorb light in the infrared band. Alternatively, the graphene quantum dot layer 34 may be configured to absorb light in both the visible light band and the infrared band in order to detect light in the visible light band remaining without being completely absorbed by the semiconductor layer 33 .

7 is a cross-sectional view schematically showing a structure of an optical sensor according to another embodiment. Referring to FIG. 7 , the photosensor 30 ′ includes a first electrode 11 , a photodetection layer 32 ′ disposed on the first electrode 11 , and a second photodetection layer 32 ′ disposed on the photodetection layer 32 ′. An electrode 14 may be included. In addition, the photodetection layer 32 ′ may include a semiconductor layer 33 disposed on the first electrode 11 and a graphene quantum dot layer 34 disposed on the semiconductor layer 33 . The semiconductor layer 33 may include a first semiconductor layer 33a disposed on the first electrode 11 and a second semiconductor layer 33b disposed on the first semiconductor layer 33a. Here, the first semiconductor layer 33a is doped with a first conductivity type and the second semiconductor layer 33b is doped with a second conductivity type electrically opposite to the first conductivity type. For example, when the first electrode 11 is a cathode and the second electrode 14 is an anode, the first semiconductor layer 33a is doped n-type and the second semiconductor layer 33b is p-type. may be doped. Conversely, when the first electrode 11 is an anode and the second electrode 14 is a cathode, the first semiconductor layer 33a is doped p-type and the second semiconductor layer 33b is doped n-type. can be Accordingly, according to the present embodiment, the semiconductor layer 33 has a PN junction structure. Since the semiconductor layer 33 has a PN junction structure, a built-in potential barrier may be additionally formed in the semiconductor layer 33 . Therefore, the dark current can be further suppressed.

8 is a cross-sectional view schematically illustrating a structure of an optical sensor according to another embodiment. Referring to FIG. 8 , the photosensor 40 includes a first electrode 11 , a photodetection layer 42 disposed on the first electrode 11 , and a second electrode 14 disposed on the photodetection layer 42 . ) may be included. The photo-detecting layer 42 may include a plurality of semiconductor layers 43 and 43 ′ and a plurality of graphene quantum dot layers 44 alternately disposed between the first electrode 11 and the second electrode 14 . have.

Here, the first semiconductor layer 43 disposed directly on the first electrode 11 may be made of the semiconductor material described with reference to FIG. 5 . That is, the energy difference between the LUMO energy level of the graphene quantum dot layer 44 and the valence band of the first semiconductor layer 43 is small, and the work function of the first electrode 11 and the conduction band of the first semiconductor layer 43 are small. The first semiconductor layer 43 may be selected such that the energy difference between . For example, the energy difference between the work function of the first electrode 11 and the conduction band of the first semiconductor layer 43 is the LUMO energy level of the graphene quantum dot layer 44 and the valence band of the first semiconductor layer 43 . It can be greater than the energy difference with On the other hand, the second semiconductor layer 43 ′ disposed between two adjacent graphene quantum dot layers 44 is the highest occupied molecule orbital (HOMO) of the graphene quantum dot layer 44 so that electrons and holes can easily move. The energy difference between the energy level and the conduction band of the second semiconductor layer 43' is selected to be small. For example, the energy difference between the HOMO energy level of the graphene quantum dot layer 44 and the conduction band of the second semiconductor layer 43 ′ is the work function of the first electrode 11 and the conduction band of the first semiconductor layer 43 . It may be smaller than the energy difference with . Also, the thickness of each second semiconductor layer 43 ′ may be selected such that tunneling occurs in each second semiconductor layer 43 ′.

The graphene quantum dot layer 44 may be the same as the photodetection layers 12 and 22 described in FIGS. 1 and 3 . The plurality of semiconductor layers 43 and 43 ′ and the plurality of graphene quantum dot layers 44 may form a multi-quantum well (MQW) structure. For example, the plurality of semiconductor layers 43 and 43 ′ may serve as barrier layers and the plurality of graphene quantum dot layers 44 may serve as quantum well layers.

The above-described optical sensors 10 , 20 , 30 , 30 ′ and 40 may be manufactured as individual optical sensing electronic devices, such as photodiodes, and mounted in an electronic device. In addition, an image sensor for photographing a two-dimensional image may be manufactured using the above-described optical sensors 10 , 20 , 30 ', and 40 .

For example, FIG. 9A is a cross-sectional view schematically illustrating one pixel structure of an image sensor according to an exemplary embodiment. Referring to FIG. 9A , one pixel of the image sensor 100 includes a signal processing layer 110 , a first electrode 11 , a light sensing layer 130 , a second electrode 14 , and a transparent protective layer 120 . may include

The light sensing layer 130 may include a plurality of photodetection layers 12a, 12b, 12c, and 12d arranged in parallel on the same layer. For example, the photodetection layers 12a , 12b , 12c , and 12d may have the same structure as the photodetection layer 12 shown in FIG. 1 . That is, the first photodetection layer 12a includes a first graphene quantum dot layer having a plurality of first graphene quantum dots 15a bonded to the first functional group A, and the second photodetection layer 12b ) includes a second graphene quantum dot layer having a plurality of second graphene quantum dots 15b bonded to a second functional group (B), and the third photodetection layer 12c includes a third functional group (C) and A third graphene quantum dot layer having a plurality of combined third graphene quantum dots 15c, and the fourth photodetection layer 12d is a plurality of fourth graphene quantum dots bonded to a fourth functional group (D) It may include a fourth graphene quantum dot layer having (15d). In FIG. 9A, for convenience only, the first to fourth photodetecting layers 12a, 12b, 12c, and 12d are illustrated as including only one type of the first to fourth graphene quantum dots 15a, 15b, 15c, and 15d, respectively. However, it is also possible that each of the first to fourth photodetecting layers 12a, 12b, 12c, and 12d includes two or more types of graphene quantum dots.

The first functional group (A) of the first graphene quantum dots (15a) is selected to absorb light in the first wavelength band, and the second functional group (B) of the second graphene quantum dots (15b) is light in the second wavelength band is selected to absorb light, the third functional group (C) of the third graphene quantum dot (15c) is selected to absorb light in the third wavelength band, and the fourth functional group (D) of the fourth graphene quantum dot (15d) is It may be selected to absorb light in the fourth wavelength band. In addition, the sizes of the first to fourth graphene quantum dots 15a, 15b, 15c, and 15d may be selected differently to be appropriate for each absorption wavelength band. In this structure, the first photodetection layer 12a detects light in the first wavelength band, the second photodetection layer 12b detects light in the first wavelength band, and the third photodetection layer 12c detects the light of the third wavelength band, and the fourth photodetection layer 12d detects the light of the fourth wavelength band. For example, the first photodetection layer 12a detects blue light, the second photodetection layer 12b detects green light, the third photodetection layer 12c detects red light, and the fourth photodetection layer 12c detects red light. Layer 12d may be configured to detect infrared light. In particular, the fourth photodetection layer 12d may detect a near-infrared wavelength band in the range of, for example, about 800 nm to about 900 nm. To this end, the fourth graphene quantum dot 15d may be configured to have a bandgap of about 1.38 eV or less.

The first electrode 11 is a pixel electrode, and a plurality of first electrodes 11 respectively connected to the first to fourth photodetection layers 12a, 12b, 12c, and 12d may be disposed. The second electrode 14 is a common electrode, and one second electrode 14 may be connected to the first to fourth photodetecting layers 12a, 12b, 12c, and 12d. In addition, the second electrode 14 may be a transparent electrode that is transparent to visible light and infrared light. A transparent protective layer 120 having insulating properties may be disposed on the second electrode 14 . In addition, the signal processing layer 110 serves to process the optical signal detected by the optical sensing layer 130 into an electrical signal. To this end, the signal processing layer 110 is respectively connected to the plurality of first electrodes 11 . The signal processing layer 110 may include, for example, an integrated circuit.

In the image sensor 100 illustrated in FIG. 9A , regions corresponding to the first to fourth photodetection layers 12a, 12b, 12c, and 12d are sub-pixels 100a, 100b, 100c, and 100d, and each One group including the sub-pixels 100a, 100b, 100c, and 100d may be a pixel. For example, the first sub-pixel 100a is a region that senses light of a first wavelength band within one pixel, and the second sub-pixel 100b senses light of a second wavelength band within one pixel. The third sub-pixel 100c is a region that detects light of a third wavelength band within one pixel, and the fourth sub-pixel 100d senses light of a fourth wavelength band within one pixel. is an area to 9B and 9C are plan views illustrating an arrangement of sub-pixels 100a, 100b, 100c, and 100d in one pixel of the image sensor 100 illustrated in FIG. 9A . As shown in FIG. 9B , the sub-pixels 100a, 100b, 100c, and 100d may be arranged in a line. Alternatively, as shown in FIG. 9C , the sub-pixels 100a, 100b, 100c, and 100d may be two-dimensionally arranged in a 2×2 matrix. Since the image sensor 100 according to the present embodiment has high detection efficiency with respect to light in the infrared band, as shown in FIGS. 9B and 9C , the sub-pixels 100a , 100b , 100c , and 100d have the same size. It is possible to configure

10 is a cross-sectional view schematically illustrating one pixel structure of the image sensor 200 according to another exemplary embodiment. Referring to FIG. 10 , the light sensing layer 130 may include a plurality of photodetection layers 22a , 22b , 22c , and 22d arranged in parallel on the same layer. For example, the photodetection layers 22a , 22b , 22c , and 22d may have the same structure as the photodetection layer 22 shown in FIG. 3 . That is, each of the photodetecting layers 22a, 22b, 22c, and 22d includes at least a plurality of first to fourth graphene quantum dots 15a, 15b, 15c, each absorbing light of different first to fourth wavelength bands, respectively. 15d) may be included. For example, each of the photodetecting layers 22a, 22b, 22c, and 22d may include a plurality of first graphene quantum dots 15a bonded to a first functional group (A), and a plurality of second graphene quantum dots bonded to a second functional group (B). to include a graphene quantum dot 15b, a plurality of third graphene quantum dots 15c bonded to a third functional group (C), and a plurality of fourth graphene quantum dots 15c bonded to a fourth functional group (D). can Accordingly, the light detection layers 22a , 22b , 22c , and 22d in the light sensing layer 130 may be identical to each other and may be sensitive to blue light, green light, red light, and infrared light.

In addition, the image sensor 200 may further include a color filter layer 140 disposed between the second electrode 14 and the transparent protective layer 120 . The color filter layer 140 includes, for example, a first color filter 141 that transmits only light of a first wavelength band, a second color filter 142 that transmits only light of a second wavelength band, and a third wavelength band of light. It may include a third color filter 143 that transmits only light and a fourth color filter 144 that transmits only light of the fourth wavelength band. For example, the first color filter 141 transmits light in a red wavelength band, the second color filter 142 transmits light in a green wavelength band, and the third color filter 143 transmits light in a blue wavelength band. The light may be transmitted, and the fourth color filter 144 may transmit light in the near-infrared wavelength band. Alternatively, the first color filter 141 transmits cyan light, the second color filter 142 transmits magenta light, the third color filter 143 transmits yellow light, and the fourth color filter 144 transmits yellow light. ) may transmit near-infrared light.

The first to fourth photodetecting layers 22a , 22b , 22c , and 22d may be disposed to correspond to the first to fourth color filters 141 , 142 , 143 , and 144 , respectively. For example, the first photodetection layer 22a detects light that has passed through the first color filter 141 , and the second photodetection layer 22b detects light that has passed through the second color filter 142 . and the third photodetection layer 22c detects the light passing through the third color filter 143 and the fourth photodetection layer 22d detects the light passing through the fourth color filter 144 have.

On the other hand, the light sensing layer 130 of the image sensor 100 shown in FIG. 9A is the photodetector layer 32 shown in FIG. 5 instead of the photodetector layer 12 shown in FIG. The photodetector layer 32' or the photodetection layer 40 shown in FIG. 8 may be included. Similarly, the light-sensing layer 130 of the image sensor 200 shown in FIG. 10 is the photo-sensing layer 32 shown in FIG. 5, instead of the photo-sensing layer 22 shown in FIG. 3, The photodetector layer 32' or the photodetection layer 40 shown in FIG. 8 may be included.

11 is a cross-sectional view schematically illustrating a structure of one pixel of an image sensor according to another exemplary embodiment. Referring to FIG. 11 , the light sensing layer 130 of the image sensor 300 includes first to third photodetection layers 131 , 132 and 133 for detecting light in the visible light band and the first to third photodetecting layers 131 , 132 and 133 for detecting light in the infrared band. 4 may include a photodetector layer 134 . For example, the first to third photodetection layers 131 , 132 , and 133 may include a conventional semiconductor material such as silicon, a compound semiconductor material, an organic semiconductor material, or a two-dimensional semiconductor having a bandgap and a two-dimensional crystal structure. It can be made of material. The fourth photodetection layer 134 may have, for example, the same structure as the photodetection layer 32 shown in FIG. 5 . That is, the fourth photodetection layer 134 may include a semiconductor layer 33 disposed on the first electrode 11 and a graphene quantum dot layer 34 disposed on the semiconductor layer 33 . The graphene quantum dots in the graphene quantum dot layer 34 may be coupled to the fourth functional group (D) and configured to react sensitively to infrared rays. For example, graphene quantum dots bonded to the fourth functional group (D) may have a band gap of 1.38 eV or less.

The semiconductor layer 33 of the fourth photodetection layer 134 may be made of the same semiconductor material as the semiconductor material constituting the first to third photodetection layers 131 , 132 , and 133 . In this case, after the semiconductor material is laminated on the entire region of the first to fourth photodetection layers 131 , 132 , 133 and 134 , the semiconductor material formed in the region of the fourth photodetection layer 134 is etched to a partial depth. Then, the graphene quantum dot layer 34 may be formed on the semiconductor material remaining after being etched.

Instead, only the first to third photodetecting layers 131 , 132 and 133 are made of a semiconductor material, and the fourth photodetecting layer 134 is the photodetecting layer 12 shown in FIG. 1 , shown in FIG. 3 . It may be formed in the same structure as the photo-detecting layer 22 , the photo-detecting layer 32 ′ shown in FIG. 7 , or the photo-detecting layer 42 shown in FIG. 8 . In this case, after the semiconductor material is laminated on the entire area of the first to fourth photodetection layers 131 , 132 , 133 and 134 , the semiconductor material formed in the region of the fourth photodetection layer 134 is completely etched and removed. Next, in the region of the fourth photodetection layer 134 , the photodetection layer 22 shown in FIG. 3 , the photodetection layer 32′ shown in FIG. 7 , or the photodetection layer 42 shown in FIG. 8 . can form.

The above-described image sensors 100 , 200 , and 300 may have high detection efficiency for light in a visible light band and an infrared band using graphene quantum dots to which functional groups are bonded. In particular, compared to the case of using a silicon semiconductor, the detection efficiency for light in the infrared band may be improved. In addition, it is possible to effectively suppress the dark current generated while light is not incident. Accordingly, it is possible to increase the degree of freedom for arrangement or size selection of sub-pixels, and to broaden the range of products applied to the image sensors 100 , 200 , and 300 . For example, the image sensors 100 , 200 , and 300 may naturally obtain a clear image in an environment with a high amount of light, and may obtain a high-quality image by using near-infrared light along with visible light even in a low-illuminance environment with a small amount of light.

Also, the image sensors 100 , 200 , and 300 may be applied to sensing an iris image of a person. In the long wavelength band (far infrared rays), it is difficult to distinguish the difference between the iris and the sclera, so it is difficult to recognize the iris by using a photodetector in the long wavelength band. Conversely, in the short wavelength (visible light) band, the iris pattern recognition error may occur because light is reflected from the region around the iris. For example, in the case of dark brown or brown-based pupils, the iris may be recognized using near-infrared light, but may be difficult to recognize with visible light. On the other hand, in the case of blue or green pupils, the iris may be recognized using near-infrared light, and the iris may also be recognized with visible light. Accordingly, the iris can be recognized using near-infrared rays that can be applied to most pupils. Accordingly, the image sensors 100 , 200 , and 300 according to the present embodiment having high detection efficiency for light in the near-infrared band may be suitably used for imaging the iris.

In addition, since sensitivity (reactivity) to infrared rays or quantum efficiency is high, the size of the light sensing layer 130 can be reduced. Accordingly, the image sensors 100 , 200 , and 300 of the present embodiment may be employed in a slim and small electronic device such as a smart phone. When the image sensors 100 , 200 , and 300 of the present embodiment are employed in a smartphone, the iris recognition rate can be increased and the accuracy can be increased. Accordingly, the image sensors 100 , 200 , and 300 according to the present embodiment can be usefully used for self-authentication through iris authentication.

Although the above-described optical sensor and image sensor including the graphene quantum dots have been described with reference to the embodiment shown in the drawings, this is merely an example, and those of ordinary skill in the art may perform various modifications and equivalent other methods therefrom. It will be appreciated that embodiments are possible. Therefore, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense. The scope of the present invention is indicated in the claims rather than the foregoing description, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

10, 20, 30, 30', 40.....Light sensor 11, 14...Electrode
12, 22, 32, 32', 42.....Photodetection layer 34, 44...Graphene quantum dot layer
33, 33a, 33b, 43., 43'....Semiconductor layer 15...Graphene quantum dots
16, A, B, C.....Functional groups 100, 200, 300.....Image sensor
110.....Signal processing layer 120.....Transparent protective layer
130.....Light sensing layer 140.....Color filter layer
141, 142, 143, 144.....Color filter

Claims (35)

a first electrode;
a photodetector layer disposed on the first electrode; and
a second electrode disposed on the photo-detecting layer;
The photodetection layer includes a graphene quantum dot layer having a plurality of first graphene quantum dots bonded to a first functional group and a plurality of second graphene quantum dots bonded to a second functional group different from the first functional group,
The first functional group is bonded to at least one of the carbons located at the edge of each first graphene quantum dot, the second functional group is bonded to at least one of the carbons located at the edge of each second graphene quantum dot,
The first functional group and the second functional group are -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C=O)-, -F, - Among H, -CO-N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine, aniline, and polyethylene glycol (PEG) An optical sensor comprising at least one. The method of claim 1,
The first functional group is bonded to at least one of the carbons disposed at the edge of each first graphene quantum dot and the second functional group is bonded to at least one of the carbons disposed at the edge of each second graphene quantum dot. light sensor. The method of claim 1,
The first graphene quantum dot is configured to absorb light of a first wavelength band, and the second graphene quantum dot is configured to absorb light of a second wavelength band different from the first wavelength band. 4. The method of claim 3,
The graphene quantum dot layer further includes a plurality of third graphene quantum dots combined with a third functional group different from the first and second functional groups, wherein the third graphene quantum dots are third different from the first and second wavelength bands. configured to absorb light in a wavelength band,
The third functional group is bonded to at least one of the carbons located at the edge of each third graphene quantum dot,
The third functional group is -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C=O)-, -F, -H, -CO- N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine (alkylamine), aniline (aniline), and PEG (polyethylene glycol) comprising at least one light sensor. delete The method of claim 1,
The first graphene quantum dots have a first size and the second graphene quantum dots have a second size different from the first size. The method of claim 1,
The photodetector layer has a thickness in the range of 50 nm to 100 um. The method of claim 1,
The photodetector layer further comprises a semiconductor layer disposed between the first electrode and the graphene quantum dot layer. 9. The method of claim 8,
The semiconductor layer includes at least one semiconductor material from among a semiconductor material including silicon, a compound semiconductor material, an organic semiconductor material, and a two-dimensional material having a bandgap and a two-dimensional crystal structure, wherein the semiconductor material is the semiconductor layer. and a photosensor selected such that a Schottky barrier is formed between the first electrode. 10. The method of claim 9,
An energy difference between a lowest unoccupied molecular orbital (LUMO) energy level of the graphene quantum dot layer and a valence band of the semiconductor layer is smaller than an energy difference between a work function of the first electrode and a conduction band of the semiconductor layer. 10. The method of claim 9,
The two-dimensional material is an optical sensor comprising a transition metal dichalcogenide, which is a compound of a transition metal and a chalcogen element. 12. The method of claim 11,
The transition metal includes at least one of tin (Sn), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), hafnium (Hf), titanium (Ti), and rhenium (Re), and , The chalcogen element is a photosensor comprising at least one of sulfur (S), selenium (Se), and tellurium (Te). 9. The method of claim 8,
The semiconductor layer includes a first semiconductor layer disposed over the first electrode and a second semiconductor layer disposed over the first semiconductor layer, wherein the first semiconductor layer is doped to a first conductivity type and the second semiconductor layer is is doped with a second conductivity type that is electrically opposite to the first conductivity type. The method of claim 1,
The second electrode is a transparent electrode having a transmittance for light of a wavelength band to be detected. a first electrode;
a semiconductor layer disposed on the first electrode;
a graphene quantum dot layer disposed on the semiconductor layer; and
a second electrode disposed on the graphene quantum dot layer;
The graphene quantum dot layer includes a plurality of first graphene quantum dots bonded to a first functional group,
the material of the semiconductor layer is selected such that a Schottky barrier is formed between the semiconductor layer and the first electrode;
The first functional group is bonded to at least one of the carbons located at the edge of each first graphene quantum dot,
The first functional group is -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C=O)-, -F, -H, -CO- N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine (alkylamine), aniline (aniline), and PEG (polyethylene glycol) comprising at least one light sensor. 16. The method of claim 15,
An energy difference between the LUMO energy level of the graphene quantum dot layer and the valence band of the semiconductor layer is smaller than an energy difference between the work function of the first electrode and the conduction band of the semiconductor layer. 16. The method of claim 15,
The graphene quantum dot layer further includes a plurality of second graphene quantum dots combined with a second functional group different from the first functional group,
The first graphene quantum dots are configured to absorb light of a first wavelength band and the second graphene quantum dots are configured to absorb light of a second wavelength band different from the first wavelength band,
The second functional group is bonded to at least one of the carbons located at the edge of each second graphene quantum dot,
The second functional group is -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C=O)-, -F, -H, -CO- N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine (alkylamine), aniline (aniline), and PEG (polyethylene glycol) comprising at least one light sensor. delete 18. The method of claim 17,
The first graphene quantum dots have a first size and the second graphene quantum dots have a second size different from the first size. 16. The method of claim 15,
The semiconductor layer includes at least one semiconductor material from among a semiconductor material including silicon, a compound semiconductor material, an organic semiconductor material, and a two-dimensional material having a band gap and a two-dimensional crystal structure. 21. The method of claim 20,
The two-dimensional material includes a transition metal dichalcogenide, which is a compound of a transition metal and a chalcogen element,
The transition metal includes at least one of tin (Sn), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), hafnium (Hf), titanium (Ti), and rhenium (Re), and , The chalcogen element is a photosensor comprising at least one of sulfur (S), selenium (Se), and tellurium (Te). 16. The method of claim 15,
The semiconductor layer includes a first semiconductor layer disposed over the first electrode and a second semiconductor layer disposed over the first semiconductor layer, wherein the first semiconductor layer is doped to a first conductivity type and the second semiconductor layer is is doped with a second conductivity type that is electrically opposite to the first conductivity type. 16. The method of claim 15,
The second electrode is a transparent electrode having a transmittance for light of a wavelength band to be detected. a first electrode and a second electrode disposed to face each other; and
Includes; a plurality of semiconductor layers and a plurality of graphene quantum dot layers alternately disposed between the first electrode and the second electrode;
The graphene quantum dot layer includes a plurality of first graphene quantum dots bonded to a first functional group,
The plurality of semiconductor layers includes a first semiconductor layer disposed on the first electrode and a second semiconductor layer disposed between two graphene quantum dot layers,
the material of the first semiconductor layer is selected such that a Schottky barrier is formed between the semiconductor layer and the first electrode;
The first functional group is bonded to at least one of the carbons located at the edge of each first graphene quantum dot,
The first functional group is -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C=O)-, -F, -H, -CO- N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine (alkylamine), aniline (aniline), and PEG (polyethylene glycol) comprising at least one light sensor. 25. The method of claim 24,
An energy difference between the LUMO energy level of the graphene quantum dot layer and the valence band of the first semiconductor layer is smaller than an energy difference between the work function of the first electrode and the conduction band of the first semiconductor layer. 26. The method of claim 25,
The energy difference between the highest occupied molecule orbital (HOMO) energy level of the graphene quantum dot layer and the conduction band of the second semiconductor layer is smaller than the energy difference between the work function of the first electrode and the conduction band of the first semiconductor layer. sensor. 25. The method of claim 24,
The graphene quantum dot layer further includes a plurality of second graphene quantum dots combined with a second functional group different from the first functional group,
The first graphene quantum dots are configured to absorb light of a first wavelength band and the second graphene quantum dots are configured to absorb light of a second wavelength band different from the first wavelength band,
The second functional group is bonded to at least one of the carbons located at the edge of each second graphene quantum dot,
The second functional group is -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C=O)-, -F, -H, -CO- N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine (alkylamine), aniline (aniline), and PEG (polyethylene glycol) comprising at least one light sensor. delete 25. The method of claim 24,
The semiconductor layer includes at least one semiconductor material from among a semiconductor material including silicon, a compound semiconductor material, an organic semiconductor material, and a two-dimensional material having a band gap and a two-dimensional crystal structure. 30. The method of claim 29,
The two-dimensional material includes a transition metal dichalcogenide, which is a compound of a transition metal and a chalcogen element,
The transition metal includes at least one of tin (Sn), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), hafnium (Hf), titanium (Ti), and rhenium (Re), and , The chalcogen element is a photosensor comprising at least one of sulfur (S), selenium (Se), and tellurium (Te). 25. The method of claim 24,
The photosensor wherein the thickness of each second semiconductor layer is selected such that tunneling occurs in each of the second semiconductor layers. 25. The method of claim 24,
The second electrode is a transparent electrode having a transmittance for light of a wavelength band to be detected. light sensing layer; and
and a signal processing layer that processes the optical signal detected by the optical sensing layer into an electrical signal;
The light sensing layer includes a first photodetection layer that detects light of a first wavelength band, and a second detection layer that detects light of a second wavelength band different from the first wavelength band,
The first photodetection layer includes a first graphene quantum dot layer having a plurality of first graphene quantum dots bonded to a first functional group,
The second photodetection layer includes a second graphene quantum dot layer including a plurality of second graphene quantum dots bonded to a second functional group different from the first functional group,
The first functional group is bonded to at least one of the carbons located at the edge of each first graphene quantum dot, the second functional group is bonded to at least one of the carbons located at the edge of each second graphene quantum dot,
The first functional group and the second functional group are -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C=O)-, -F, - Among H, -CO-N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine, aniline, and polyethylene glycol (PEG) An image sensor comprising at least one. 34. The method of claim 33,
The light sensing layer includes a third graphene quantum dot layer having a plurality of third graphene quantum dots bonded to a third functional group different from the first and second functional groups, and a fourth functional group different from the first to third functional groups. Further comprising a fourth graphene quantum dot layer having a plurality of fourth graphene quantum dots combined with,
The third functional group is bonded to at least one of the carbons located at the edge of each third graphene quantum dot, and the fourth functional group is bonded to at least one of the carbons located at the edge of each fourth graphene quantum dot,
The third functional group and the fourth functional group are -NO ₂ , -NH ₂ , -CH ₃ , -OH, -COOH, =O, -CHO, -COCH ₃ , -(C=O)-, -F, - Among H, -CO-N(CH ₃ ) ₂ , -CH ₂ -OH, -CO-NH ₂ , -N(CH ₃ ) ₂ , alkylamine, aniline, and polyethylene glycol (PEG) An image sensor comprising at least one. 35. The method of claim 34,
An image sensor in which sizes of the first to fourth graphene quantum dots are different from each other.

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